RTV Silicone failed me again!
 

I have not had any good luck using RTV on any plastic tops. I havent had this problem untill recently when my chipset block leaked a few months ago, then just last night my pelt block leaked and luckily both times everything survived.

Has anyone else had any problems with it? I am using normal clear RTV silicone.

I also opened my gpu block up wich has a little more surface area of bonding and I can see that it looks like the silicone has started to be eaten through and is discolored on the innar edge.

This is mainly a advisory to be careful when using this stuff with plastic tops, I have used it with metal tops with no problems in the past.

Jon

Hum... here's a crazy idea: rough up the plastic with 600 grit sandpaper (mask the area that you want to keep clear).

The leak is between the plastic and the RTV, right?

Also, you might consider upgrading to another RTV, namely engine gasket makers. anything that's more resistant, even if it's black, or blue.

These are just suggestions, nothing that I've tried.

Havn't had a problem with it. I have used it in dozens of blocks with Acrylic tops. Hell the stuff is used in car engines! Odd indeed.

Maybe you could enlighten us to your technique jaydee?

How thick?

Tighten right away? Or wait a bit?

Cover entire surface, or just a small bead?

How long before adding water?

Very very thin.

Right away.

Entire surface just like you would thermal compound on a CPU.

As long as it takes to tighten the screws, hook up the hoses, and turn the pump on and fill the system. ~10mins.

EDIT: I also used clear silicon on my Direct Die Cooler. All acrylic. :shrug:

What is the recommended curing time for the RTV sealant? It should say on the tube... Keep in mind that curing time will vary with temperature, and if it's not warm enough then it will take very long or may not cure at all.

i use engine RTV sealant works like a charm

make sure that you dont crank down on the screws too much after you apply the RTV, and also DO NOT retighten, that is the biggest mistake i have seen. It friking says on the tube doesnt need retightening, so dont do it. If you do do it then it stresses the RTV and that isnt good

24hrs usually. Dosn't need to cure to be water proof though. The biggest concern is getting the top mounting screws close enough together to apply a nice even pressure across the block top. My last few blocks used with silicon just bearly leaked even with NO sealant. I always test run them with no sealant to see where the majority of the water will come out and then if needed add another screw there.

Lately though I have been using nothing but O-rings. Only way to go if your capable of it.

One note on using RTV...

Let it set up for about 30 minutes BEFORE tighening down those screws. This lets the RTV form enough of a cured "skin" to make a true gasket. If you tighten down the screws all the way you are pushing out the sealant and allowing possible leaks. You WANT that RTV to be compressed like a gasket and not squished out like grease.

This technique has worked well for me in the past on automotive as well as water block construction.

On my current reservior, I have a gasket that was created simply by putting RTV in a home made injection mold (two pieces of acrylic with a milled relief and injection holes)... I let it cure 48 hours as it didn't have much area exposed to the air. After removing it I let it cure another 24 hours outside the mold. I now have a gasket that is about 1/16" thick and is compressable and reusable. :D

Disagree. Thinner the better. Less pressure on the sealant to make a leak. The less gap between the top and the base the better.

Jaydee116,

I disagree right back... :p

If you compress the sealant all the way BEFORE it sets up... you are NOT getting any true compression... but simply spreading it out and forcing it out of the spaces that are truely flush. Any areas that have a gap will have sealant, but will NOT have a compressed gasket seal.

I don't know about you... but when I use sealant it's usually because a gasket does not exist (o-ring, or any other type). So in essence I am using the sealant AS a gasket.

When using a sealant in place of a gasket... you should treat it as such. Put the parts together... yes... let the sealant create a gasket by letting it "skin" 10-15 minutes at least... THEN tighen everything down.

RTV when used in automotive applications says you can run water through the system right away... but I have had leaks when parts are torqued down before the sealant has set up enough to create a gasket. So my method is based entirely upon my personal experience. :D

Well as in ocforums I have posted a similar thread, and its basicly suggesting that its the brand that I am using, and like you said MMZ I have been doing it like jaydee except I have been letting it cure for 24hrs before any use.

On my latest block, the distance between screws is greater than 2" wich that could be a problem although I am using copper base and 1/2" lexan for a top.

Ill be using O-rings now, This thread is mostly a word of warning to people using it. Also because I might run into places where I need it.

Jon

RTV Silicon is an ADHESIVE. You need to apply it like one. The only way it makes a good seal is my clamping it tight. Your not squishing all the sealant out. If that is the case I would have had over 50 (and dozens of re-seals) blocks leaking over the years. I have to PRY my tops off when I need to take it off.
Exactly, but not like a O-ring or a standard gasket. It is an adhesive. Says it right on the container.
If you let it skin then it isn't going to adhere properly and it will not dry properly. If you want to do that then use a gasket maker version. It needs to adhere to both sides in order to make a proper seal. That is why you should sand a smooth surface like Acrylic or Lexan because to surface is TO smooth and it will not adhere well. That is why it will leak on the acrylic side and not the metal side.
Then your doing something wrong. I go through 24 tubes of the stuff a job and about 10-15 jobs a year over the last 7 years and our company does over 40 jobs a year and we don't have any leaking problems. We apply a 20 year warranty to all leaks to boot. I think we have the process down pretty good and it is the same process I use on my blocks until now that I started using O-rings.

hrmmm...

/me gives up... :cry:

I must be wrong... maybe it's because I never sanded the Acrylic. :shrug: That's why it wasn't sticking... but using it as a gasket has worked. Go figger. :p

I will have to rethink my future projects. Thanks for clearing that up for me Jaydee116

*Hugs*

It occurs to me that you are both using RTV to do the same job, just in different ways. MMZ's is using it to make a gasket, while jaydee is using it more to glue the two pieces together. (That's how I'm reading it at least)

But they both work, so why quibble?

whats wrong with using epoxy that dries clear, as epoxies give best adhesive properties if they are kept under pressure during drying.

JoeKamel,

You are probably right... my method still uses the RTV as an adheasive, but the difference is that I let it "skin" by not torquing down the parts... Jaydee does. After mine "skins" and I torque it down, it's still in the wet adheasive stage in between the two "skins".

I'm not quibbling (at least not trying to) ... just giving my experience... and learning from others in the process. :D

Pureh20,

Probably nothing... however most epoxies are more rigid and will not allow for any flexing before breaking a seal. Not that these parts flex much, but that is the difference. :p

Epoxy can absorb water, its brittle and dries hard too.

thats mainly the problem.

Jon

Hey MMZ whatever works works, not trying to argue. The way I do it is how the company brand (Liquid Lightning) that we use at work told us how to apply it. They said if it doesn't get pressed into place it will not seal properly because they way it seals is by sticking to the parts. They said to seal a seam you apply a bead and then use your finger to spread/press it into place. They said to make a seal in a gutter splice put a bead in the splice smooth it out and then clamp the splice together (we use rivits or screws).

Hasn;t failed me or or the company I work for so that is how I will continue to use it. :)

umm.. no epoxy dosnt absorb water, im doing a boat building course, why would so many people use epoxy coatings to seal the timber of their boats if it absorbs water ? :rolleyes:

If you must use a glue / sealant then the 5min araldite epoxy is pretty good as it remains a little rubbery when cured. You have to be very quick with it though as the 5 min cure time is a bit of a exaggeration..

I've used all sorts of quality specific silicon sealants in my job (motorsport) and personally I would NEVER trust any of them to seal anything water cooled in my PC.

Just thought I would chip in, not that I have had much experience. I've tried three blocks in a similar technique to Jaydee and no problems with leaks, In fact I can't get the tops off at all now. Tried hammering a really thin screw driver between the copper and plastic and still no luck

Have you checked that both surfaces are perfectly flat and uniform with no scratches etc. ?

Both surfaces need to be parallel for Silicone selants to work (Im pretty sure this varys between selants but the ones i use do not require time to cure before torqueing up.)

You dont want to use expoxy to seal things, thats for joining things perminantly;)

Despite all that for plastic tops you need to be using a o-ring or gasket to be safe.

To the epoxy argument, there are hundreds of types of epoxy. All vary in what they can do.

Never used RTV Silicone/silicon sealant in a waterblock (only been making them for a month) but maybe the reason some people dont have much luck is the lack of silicone in acrylic? as rtv silicone sticks best to items with silicone in them (or hard objects) acrylic is slightly "Oily". As an experiment try gluing an item to Al and another to Glass and see how hard it is to get the silicone off the Glass!. Another observation i've made with it is the difficulty in getting rtv off piston heads in engines (High silicone content)... My 0.2c Keep up the good work :beer:

make a thin neoprene gasket that functions like an o ring, but is not covering the whole plate.. that way it will still look sexy and also b 100% waterproof... this is my plan for my future? #rotors

You may have a point to some extent, obviously silicone sealant will bond more readily with some materials. But I think the surface condition is what's more important. Glass is usually very smooth, so it won't bond well. Metals often aren't so smooth, especially the rough cast pieces that are usually sealed with RTV in automotive applications.
And just for future reference, there is no silicone in cylinder heads or any other metal object for that matter. There is silicon, but there is a large difference between that and silicone. And most glasses that you'll run across are mainly composed of silica (SiO2), another silicon-based material.